Commuters driving home from a night shift are at greater risk of having a motor vehicle accident due to extended wake episodes, sleep loss and circadian misalignment. Over consecutive night shifts, driving performance may improve as the circadian system adapts to the sleep-wake schedule, or decline with the accumulation of sleep loss. The aim of this study was to investigate driving performance associated with the post night shift commute over seven consecutive night shifts. Sixty-seven subjects undertook seven simulated night shifts under laboratory conditions. Following each shift, participants performed a 20-minute simulated driving task. Driving performance was assessed using lane variability (i.e. standard deviation of lateral position), speed variability (i.e. standard deviation of speed), and the likelihood of crashing and speeding relative to a daytime drive. Lane variability, speed variability and the likelihood of crashing declined over seven consecutive night shifts. The likelihood of speeding exhibited no change. These findings indicate that driving performance improved over the seven consecutive night shifts. The trend in performance likely reflected the adaptation of the circadian system. These results indicate that relatively short sequences of night shifts that dominate most Occupational Health and Safety guidelines may not always be optimal in minimizing fatigue-related risk.
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